Biomedical electrodes are commonly used for transcutaneous monitoring of variations in electrical potential associated with muscular activity, such as the pumping of a heart, and for grounding patients during electrosurgery. One such electrode is described in coassigned U.S. Pat. No. 4,694,835, and has a flat or tabular terminal for conductively attaching the electrode to electric wire leading to some type of instrumentation, such as an electrocardiograph. The tabular terminal comprises a flat electrical conductor bonded to a nonconductive backing having a continuous coating of a suitable biocompatible pressure sensitive adhesive, thereby forming nonconductive and conductive surfaces along opposite sides of the terminal.
Typically, the electric wire has been attached to terminals of this type via an "alligator" clip having opposed pivoting metal jaws with serrated, i.e., saw-shaped, teeth for holding a terminal. The jaws are spring-loaded to a closed position for clamping the terminal between the jaws, and are movable to an open position for placing the clip on the terminal. Problems with alligator clip connections include "artifacts" in or interference with the signal from the electrode caused by movement of the clip relative to the tab, and insufficient surface contact with the electrode terminal, which among other things contributes to the difficulty with interference. Another problem is that the springs providing the closing force in alligator clips have been insufficiently strong to prevent inadvertent disconnection due, for example, to movement of the patient. This problem is particularly troublesome when the patient is being monitored by automatic or semi-automatic instruments without immediate supervision. Other problems with alligator clips include that they are made of radiopaque materials and have widely varying profiles, thereby complicating interpretation of X-ray photographs made with the clips in place. Moreover, the sharp teeth of the jaws of the alligator clip can damage the conductive layer of the electrode terminal.
Coassigned U.S. Pat. No. 4,700,997 describes a push-button actuated electrical connector comprising upper and lower jaws spring-biased to an open position where a flat biomedical electrode terminal may be placed between the jaws, and a push-button actuator slidable in a housing along the upper jaw. The push-button actuator is movable along guiding cam-type surfaces from a release position where the jaws are not forced toward one another to a closed position where the actuator compresses the jaws toward one another to clamp the terminal between the jaws. The actuator may be released by moving it to the release position with a finger.
Coassigned U.S. Pat. No. 4,061,408 describes a connector for a plate electrode used in electrosurgery employing flexible generally U-shaped sheet material, the legs of which are forced together by a lever to hold a grounding plate electrode.
U.S. Pat. Nos. 4,522,211 and 4,393,584 describe several types of medical electrode connectors employing, among other things, a "spring-type clip terminal" or terminals for attaching the connector to a medical electrode.
U.S. Pat. No. 4,550,961 describes an electrosurgical electrode connector comprising upper and lower nonconductive connector plates interconnected by a hinge, and a two-legged contact spring biasing the connector plates apart. The connector plates are held together by a releasable latch mechanism on the upper plate that engages two connector posts extending upwardly from the lower plate through a connection tab of the electrode.
U.S. Pat. No. 3,842,394 describes an electrical connector for a plate electrode used in electrosurgery comprising two separable jaws spring-biased apart, and an overcenter-type releasable locking structure for moving the jaws together to clamp the electrode. U.S. Pat. No. 3,624,590 describes a clamp for disposable ground plate electrodes used in electrosurgery comprising two jaws pivotably interconnected and spring-biased together to clamp the electrode. The jaws may be separated to release the electrode by pushing two levers extending from the jaws together.
U.S. Pat. No. 4,515,669 describes an internal connection for a tubular anode of the type used for cathodic protection. The connection includes a pair of opposing wedge blocks that are adapted to tightly wedge together to form an electrical connection. The blocks include a corresponding tongue-and-slot arrangement in the inter-engaging faces of the blocks for positioning them relative to one another.
U.S. Pat. No. 3,504,332 describes a "multi-tap" electrical connector for underground connection of a number of cables to secondary cables designed for use in electricity transmission and distribution. The connector employs a wedge member for wedging the end of each electrical cable to the body of the connector. U.S. Pat. No. 1,942,435 describes a connection for a battery terminal post employing a wedge for engaging and holding the terminal post.
U.S. Pat. No. 4,634,205 describes conductor splicing devices for splicing aerial drop wires comprising a housing having tapered passageways for receiving the wires being spliced, and a wedge for each passageway which is driven into the passageway to press the wire against insulating-piercing terminals and hold the wires in the passageway.
U.S. Pat. No. 4,696,532 describes a connector for connecting the center conductor of coaxial cable to a junction box. The connector employs an axial spring sleeve having a conical section received in a complementary conically-shaped hole in a sleeve held in the connector. The arrangement is such that if the center conductor is pulled away from the connector, the conical section of the spring sleeve is pulled further into the sleeve held in the connector, thereby increasing the clamping force holding the center conductor in the connector.
In the biomedical connectors discussed above, the strength or tenacity of the grip is substantially constant regardless of any movement of the connector or tension in the electric wire. The tenacity of the grip does not increase in such connectors when the electric wire is jerked or otherwise tensioned. Moreover, these biomedical connectors must be either manually locked on the terminal by pushing a button or lever, or they include some type of spring-biasing mechanism for biasing the connector to its locked position. Either approach has shortcomings. Manually-actuatable mechanisms may be inadvertently left unlocked, and are frequently an annoying nuisance to lock. The spring-biasing mechanism may be inadvertently forced open against the spring bias in some situations, and weak spring mechanisms may result in unacceptable connections.
In the connectors described above that are not designed for use in the medical field, the wedges or tapered members are jammed into passageways to hold wires, cables or other members in the connector, and it would be time-consuming and annoying to manually jam such wedges in a biomedical connector, which may be used in situations where time is critical and unnecessary annoyances are particularly undesirable. Generally, these wedges are not readily reversible for releasing the wire, cable or other member from the connector. In addition, these wedges are separable from the connectors, and are likely to be lost or misplaced when needed.